Here’s what the researchers found.
Reviewed by Dietitian Madeline Peck, RDN, CDN
Key Points
- Osteoarthritis (OA) is a common condition, affecting 32.5 million U.S. adults.
- Exercise and inulin, a prebiotic fiber, may help reduce knee OA pain.
- Exercise also helped improve function for those with knee OA.
Osteoarthritis (OA) is the most common type of arthritis, affecting 32.5 million U.S. adults. It’s estimated that 242 million people worldwide have symptomatic (i.e. with pain) and activity-limiting OA of the knee and/or hip. This all adds up to substantial costs in missed work days and medical expenses—a total of about $136 billion per year. Not only that, but people with debilitating OA may have a 55% increased risk of early death due to reduced levels of physical activity, comorbidities and adverse effects of medications.
Researchers are continually on the hunt for interventions for OA. Joint replacement is a common one, but before you reach that option, there are other things you can do to help reduce the pain and improve function.
Researchers from the University of Nottingham in the UK performed a study to see if supplementing with inulin, a prebiotic fiber found in plants, might have any effect on OA knee pain and function. They chose inulin because previous studies suggested that a healthy gut microbiome might improve pain and pain perception. Prebiotics feed the beneficial gut bacteria (probiotics), creating a healthy, lush microbiome. This study was published in Nutrients. Let’s break down what they found.
How Was This Study Conducted?
Researchers recruited people from two avenues: databases that people with chronic pain had registered for and agreed to be contacted by researchers for possible study inclusion, and people who responded to ads on social media. After screening candidates, researchers included a total of 136 participants with knee OA at baseline. Most of the participants were female, and the participants had an average age of 68. Out of the 136 participants at the start of the study, 117 completed the six-week study to the end.
Participants were assigned to one of four groups: inulin-only, physical activity-only, a combination of physical activity and inulin and a placebo group. The placebo group took a maltodextrin powder supplement and continued with life as usual. The inulin and maltodextrin groups did not know which supplement they were taking.
The inulin groups were instructed to take 20 grams of supplement per day, mixing it with yogurt, smoothies, breakfast cereal or a drink of choice. This dose was chosen because previous studies have shown a correlation with this amount and an improvement in the gut microbiome. Because maltodextrin is a highly-processed carbohydrate that acts like sugar in the body, that group was instructed to take 10 grams per day to avoid a blood sugar spike, and also mix it into the same foods and beverages as the inulin group.
The physical activity groups were introduced to an online platform that includes personalized exercise programs with education on OA; participants had a “kick-off” call with a physical therapist, and were expected to participate daily. The included exercises focused on strengthening the muscles in the hips and knees, and improving balance.
At baseline and after six weeks of intervention, participants underwent several assessments so that results from baseline could be compared to results after the intervention period. The physical exams were performed three times, and the average of all three was recorded. These assessments included assessing pain level, pain sensitivity (testing a participants’ pain perception of the same stimulus), lower-body function, grip test, Knee Injury and Osteoarthritis Outcome Score (KOOS) and short-chain fatty acid (SCFA) measurements.
What Did This Study Find?
At the end of six weeks, researchers found:
- The inulin-only, physical activity-only and combination groups (inulin plus physical activity) each had moderate to large effects in reducing pain compared to the placebo group.
- The physical activity groups showed improvement in pain, as well as in walking and squatting abilities.
- The inulin supplementation was associated with moderate improvements in pain and pain sensitivity.
Researchers did not find a correlation between short-chain fatty acid blood levels and pain or function. (When your gut bacteria ferment inulin, short-chain fatty acids are formed as a byproduct.) However, the researchers did find an incidental link with inulin supplementation and glucagon-like peptide 1s (GLP-1s) in the blood, which in turn, was linked with improvements in grip strength and KOOS function.
It’s important to note that these GLP-1s are not the medications prescribed for weight loss. GLP-1s are naturally produced in our bodies when we eat, as they can help regulate blood sugar. These are the hormones the researchers were measuring. Because this was an incidental finding and not a part of the original study design, researchers did not investigate this aspect any further and will save it for a future study.
As with any study, there are limitations that may affect the study’s findings. There was a high drop-out rate in the exercise groups (21%) compared to the other two groups (4%), which could reduce the strength of the findings. However, researchers point out that previous studies suggest similar findings, so they feel their results are still applicable. Due to the dropout rate, some of the findings were what researchers called underpowered. For this reason, they were unable to say whether the combination of inulin and exercise had a greater impact compared to each of the interventions on their own. Lastly, while participants were “blinded” as to which supplement they were receiving, those in the exercise groups could not be blinded. This introduces a possibility of bias and “expectancy effects.” In other words, because exercise is a common therapy for OA, they might expect the exercise to help them, which could psychologically skew their perception of the pain.
How Does This Apply to Real Life?
Exercise for osteoarthritis is a first-line option for pain relief and functional improvement. But despite its benefits, many people don’t stick with an exercise program, as shown in this study. These researchers note that a simple nutritional tweak—supplementing with inulin—may be a more viable option for many, and one that they’ll adhere to.
To reach the 20 grams of inulin that participants consumed in this study, supplementation would certainly help. But if you’d just like to add some more inulin to your diet, you’ll find this prebiotic naturally occurring in sunchokes (Jerusalem artichokes) and chicory root. It’s also added to prebiotic sodas and some cereals, snack bars and yogurts. And while inulin has many benefits, starting in the gut, it’s not for everyone.
Besides being a soluble fiber, inulin is also a fructan, a type of FODMAP. If you have IBS, fructans might be a trigger for your symptoms. And even if you don’t, it can still cause a lot of gas and bloating, especially if you don’t ease into your intake of it.
The good news is, inulin isn’t the only nutritional option for alleviating OA symptoms. There is evidence that prebiotics, probiotics and collagen supplementation may help improve OA symptoms by reducing inflammation.
Following a Mediterranean diet or a plant-based eating pattern has also been linked with reduced OA pain, increased physical function and positive biomarker changes, including lower inflammation, as have curcumin, polyphenols and omega-3s.
Our Expert Take
This study suggests that supplementing with inulin may help reduce osteoarthritis pain. Physical activity resulted in similar benefits, both alone and in combination with inulin. If your gut does not handle inulin well, find fiber types that do work for you and include probiotics from fermented foods, like yogurt, kefir and sauerkraut, to help boost your microbiome’s health. Following an anti-inflammatory eating pattern like the Mediterranean diet can help you eat a wide variety of foods loaded with prebiotic fiber, probiotics, omega-3s and polyphenols, which may help calm inflammation and support your joint health.
Comments are closed.